This invention relates generally to endoluminal stents, grafts, and/or prostheses and, more specifically, to braided stents adapted for deployment in branched lumina and processes for their manufacture.
A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called xe2x80x9cminimally invasive techniquesxe2x80x9d in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or xe2x80x9cintroducerxe2x80x9d to the site where it is required. The introducer may enter the body through the patient""s skin, or by a xe2x80x9ccut downxe2x80x9d technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of stent architectures are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these wire stent configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference, the ""771 Wallsten patent being only one example of many variations of braided stents known in the art and thus not intended as a limitation of the invention described herein later. Braided stents tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. The flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where the lumen of the vessel often becomes contorted and irregular both before and after placement of the stent.
Among the many applications for stent-grafts is for deployment in bifurcated lumen, such as for repair of abdominal aortic aneurysms (AAA). Various stent-graft configurations are known in the art for bifurcated applications, including single-piece and modular designs, graft designs fully supported by stents, and graft designs only partially supported by stents. Referring now to FIGS. 1A and 1B, there are shown the components of a modular, non-braided, bifurcated, stent 10 for use with a fully-supported graft as is fully described in U.S. Pat. No. 5,609,627 to Goicoechea et al and adapted for implantation within the aorta of a human. By xe2x80x9cfully-supportedxe2x80x9d it is meant that the graft is adapted to have stent structure underlying the graft throughout the entire length of the graft, as opposed to having extensive lengths of unsupported graft between anchoring stent portions, as will be described herein later.
As shown in FIG. 1A, stent 10 comprises a main body 12 which bifurcates into a first frustoconical leg transition 14 with a dependent first leg 16, and a second frustoconical leg transition 18. Second leg 20 is a modular component comprising a frustoconical part 22 adapted to interlock within second leg transition 18, and a depending portion 24. Frustoconical part 22 may have barbs 23 to help firmly connect second leg 20 to leg transition 18. As shown in FIG. 2, such a bifurcated stent 10 is typically implanted within the vasculature such that the main body 12 and leg transitions 14 and 18 are positioned within the aorta main portion 26 and with the dependent first leg 16 and depending portion 24 of second leg 20 each positioned within respective iliac arteries 28 and 30. Modular designs are also available wherein both legs are modular components. All of the bifurcated stents described herein, regardless of underlying structure, generally resemble the configuration shown in FIG. 2 when fully implanted.
As shown in FIGS. 1A and 1B and as fully described in the ""627 patent, the structure of stent 10 is a continuous wire zig-zag structure comprising a series of struts 32 joined at apices 34 and wound into hoops 36, with abutting hoops joined together in some manner, such as with sutures, at abutting apices. One potential disadvantage of zig-zag stent architecture is that the apices of the zig-zag structure can rub against the graft, causing wear in the graft.
Modular, fully-supported, bifurcated stent-graft designs using braided architecture are also known. Such designs typically comprise a tubular stent that is crimped or pinched together in the middle or at one end to form a septum and two smaller lumina. These two lumina can then be used as sockets for the iliac sections. The braided stents have the advantage of being very adaptable to tortuous anatomy as compared to other stent architectures. The formation of the crimp, however, can cause metal cold-work and embrittlement in the stent wires and can result in bulkiness in the bifurcation region, requiring a relatively larger deployment profile than other designs.
To overcome the potential disadvantages of modular designs, it is also known to provide one-piece or xe2x80x9cunitaryxe2x80x9d stent designs. Such known designs may be fully supported or only partially supported, such as by having anchoring stent portions only located at the end sections adjacent each opening of the graft. One piece stent designs having a zig-zag stent architecture still have the same disadvantage of potential graft wear due to rubbing of the apices. One-piece graft designs that are only partially supported have the potential disadvantage that the differences in radial strength and flexibility between the unsupported and supported regions makes the stent-grafts susceptible to kinking when navigating through tortuous lumina.
Thus, there is still a need in the art to provide a fully-stent-supported, bifurcated stent-graft that is flexible for navigation through tortuous lumina and that minimizes the risk of elements of the stent architecture creating wear in the graft covering or liner.
The invention comprises a branching stent for deployment in a lumen, the stent comprising a body that branches into a plurality of legs. At least a first leg portion of each leg comprises a discrete plurality of continuous filaments braided together and at least a first body portion of the body comprises at least one (preferably more, and more preferably all) of the continuous filaments from each discrete plurality of continuous filaments braided together. At least one of the legs or the body may further comprise a second portion thereof having a non-braided stent architecture, or each of the legs and the body may further comprise a braided stent architecture throughout the entire respective lengths thereof. The stent may be a bifurcated stent having an interface between the body and the legs with an open crotch region between the legs at the interface or a closed crotch region between the legs at the interface. A stent with a closed crotch may further comprise an open hip region.
The invention also comprises a stent for deployment in a lumen, the stent comprising a plurality of continuous filaments braided together, at least one filament comprising a tapered filament having at least one first region having a first, relatively-larger cross-sectional area and at least one second region having a second, relatively-smaller cross-sectional area. A braided stent having tapered wire according to the present invention may be a bifurcated stent or a non-bifurcated stent.
The invention also comprises a method for treating a diseased branched lumen of a human being, the branched lumen comprising a main section that branches into a plurality of branches. The method comprises the step of deploying within the branched lumen a branching stent comprising a body that branches into a plurality of legs. At least a first leg portion of each leg comprises a discrete plurality of continuous filaments braided together, and at least a first body portion of the body comprises at least one of the continuous filaments from each discrete plurality of continuous filaments braided together. The deployment step comprises deploying the body in the main section and deploying each leg within one of the branches.
The invention further comprises a process for constructing a braided, branched stent having a body and a plurality of legs, each leg comprising a discrete plurality of filaments, the process comprising the steps of: (a) braiding each plurality of filaments to individually form at least first leg portions of each of the legs; and (b) braiding at least one filament from each plurality of continuous filaments together to form a first body portion of the body. Step (a) may comprise the steps of: (i) braiding a first discrete plurality of filaments to form the first leg; and (ii) braiding a second discrete plurality of filaments to form the second leg, and step (b) may comprise braiding the first plurality of filaments and the second plurality of filaments together to form the body. Step (a) may be performed prior to step (b), or vice versa. The stent may be braided around a mandrel having a mandrel body, a first detachable mandrel leg, and a second detachable mandrel leg. In such case, step (a)(i) comprises braiding the first plurality of filaments about the first detachable mandrel leg, step (a)(ii) comprises braiding the second plurality of filaments about the second detachable mandrel leg, and step (b) comprises braiding the first plurality of filaments and second plurality of filaments together about the mandrel body.
The braiding may be performed on a braiding machine having a predetermined plurality of bobbin carriers adapted to revolve in a pattern about a longitudinal axis. A first set of bobbin carriers may be adapted to revolve in a first circumferential direction and a second set of bobbin carriers may be adapted to revolve in a second circumferential direction, each bobbin carrier adapted to carry at least one bobbin. Each bobbin is adapted to provide one or more filaments for braiding within the stent. In such case, step (a)(i) comprises using filaments from a first portion of the predetermined plurality of bobbins to braid the first leg about the first detachable mandrel leg positioned substantially along the longitudinal axis in a braiding zone. The braiding zone is defined as a conical zone defined by the filaments extending from the bobbins to the stent on the mandrel. In step (a)(ii), the process comprises using filaments from a second portion of the predetermined plurality of bobbins to braid the second leg about the second detachable mandrel leg positioned in the braiding zone. Step (b) comprises using filaments from both portions of the predetermined plurality of bobbins to braid the body about the mandrel body positioned in the braiding zone.
Thus, the process may further comprise the steps of: (A) first performing step (a)(i); (B) then removing the first portion of the predetermined plurality of bobbins from the braiding machine and removing the first mandrel leg from the braiding zone; (C) then performing step (a)(ii); (D) then returning the first portion of the predetermined plurality of bobbins to the braiding machine, attaching the first mandrel leg and the second mandrel leg to the mandrel body, and positioning the mandrel body in the braiding zone; and (E) then performing step (b). The process may instead comprise the reverse: (A) first performing step (b); (B) then removing the second portion of the predetermined plurality of bobbins from the braiding machine and attaching the first mandrel leg to the mandrel body; (C) then performing step (a)(i); (D) then returning the second portion of the predetermined plurality of bobbins to the braiding machine and removing the first portion of the predetermined plurality of bobbins from the braiding machine, attaching the second mandrel leg to the mandrel body, detaching the first mandrel leg from the mandrel body, and positioning the first leg of the stent outside the braiding zone so that the first leg does not interfere with performance of step (a)(ii); and (E) then performing step (a)(ii).
According to an alternative embodiment of the invention, a process for constructing a braided, branched stent having a body and a first and second leg, comprises: braiding a first discrete set of filaments to form the first leg using a first braiding machine for accommodating at least a first number of bobbin carriers; braiding a second discrete set of filaments to form the second leg using either the first braiding machine or another braiding machine for accommodating at least a second number of bobbin carriers; and braiding the first and second sets of filaments together to form the body using another braiding machine for accommodating at least a third number of bobbin carriers. The first and second numbers may be equal to one another and the third number may be equal to the first number plus the second number. The first, second, and third numbers may be less than a full bobbin carrier capacity of each respective braiding machine, such as the number which produces a 1:1 braiding ratio. Either the legs or body may be braided first, and a number of different braiding configurations can be developed according to this embodiment.